Polycrystalline diamond (PCD) is a super-hard, also known as superabrasive, material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. A material wholly or partly filling the interstices may be referred to as filler material. PCD may be formed in the presence of a sintering aid such as cobalt, which is capable of promoting the inter-growth of diamond grains. The sintering aid may be referred to as a solvent/catalyst material for diamond, owing to its function of dissolving diamond to some extent and catalysing its re-precipitation. A solvent/catalyst for diamond is understood to be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent/catalyst material. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt solvent/catalyst for the PCD.
PCD may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. For example, PCD elements may be used as cutting elements on drill bits used for boring into the earth in the oil and gas drilling industry. Such cutting elements for use in oil and gas drilling applications are typically formed of a layer of PCD bonded to a cemented tungsten carbide-cobalt substrate and, in many of these applications, the temperature of the PCD material may become elevated as it engages a rock formation, workpiece or body with high energy. Unfortunately, mechanical properties of PCD such as hardness and strength tend to deteriorate at high temperatures, largely as a result of residual solvent/catalyst material dispersed within it. Another major problem experienced with such cutters is the relatively low erosion resistance of the carbide substrate of the cutter. This may result in the carbide substrate being eroded very quickly during the drilling process due to mud forming from the coolants used in the drilling process and penetration of abrasive particles from the drilled rock into the carbide substrate. A worn and eroded carbide substrate cannot support the PCD layer attached thereto, with the result that the whole cutter may fail.
There is therefore a need for cemented carbide substrates for attachment to a body of PCD material having improved erosion resistance.